U.S. Pat. Nos. 5,476,572; 5,622,598; 5,635,025; 5,736,006; 5,753,075; 5,766,418; and 5,795,438 disclose methods and devices for feeding a slurry of comminuted cellulosic fibrous material to a treatment vessel that have revolutionized the art of treating comminuted cellulosic fibrous material to produce cellulose pulp. The disclosed inventions, sold under the trademark LO-LEVEL by Ahistrom Machinery Inc., of Glens Falls, N.Y., employ one or more slurry-type pumps for treating and transferring comminuted cellulosic material to one or more treatment vessels. Not since the initial development of the continuous cooking process in the 1940s and 1950s have such dramatic improvements been made to the equipment used to transfer material to a treatment vessel, for example, a continuous or batch digester. This is confirmed by the broad acceptance of this technology by the Pulping Industry.
The present invention introduces improvements to the systems described in the above patents which further simplify and enhance the effectiveness of the methods and devices disclosed in the above referenced patents. U.S. Pat. No. 5,622,598 discloses a process of using a slurry-type pump to transfer a slurry of comminuted cellulosic fibrous material to a digester, for example, by pumping the slurry to a high-pressure transfer device and then-transporting the slurry via the transfer device to one or more digesters. In particular, the method and apparatus disclosed in U.S. Pat. No. 5,622,598 provide a separate supply of liquid to the slurry pump inlet to, among other things, facilitate the transfer of comminuted cellulosic fibrous material to the pump.
Typically, this liquid is supplied by a separate storage vessel having a conduit which can discharge liquid to the inlet of the pump. A level of liquid is maintained and regulated within this vessel.
The present invention further simplifies the equipment necessary to effect the feeding of comminuted cellulosic fibrous material to a digester by, among other things, substantially eliminating the need for a separate liquor storage vessel and substantially eliminating the need for a separate level controlling vessel or tank. The liquid supplying function of this vessel or tank and the maintenance of the level of liquid within this tank are replaced by a liquor storage vessel located integrally with the conduit that passes the slurry of material from the pretreatment vessel, for example, a chip bin, to the inlet of the slurry pump.
One aspect of this invention comprises or consists of a comminuted cellulosic fibrous material treatment system, comprising (or consisting of): a digester having a comminuted cellulose material inlet at the top thereof; a first vessel, at a first pressure, containing comminuted cellulosic fibrous material, and having a top, a bottom, and an outlet adjacent the bottom; a conduit having an inlet communicating with the outlet of the first vessel, and an outlet; a second vessel, having a width dimension greater than the conduit, for receiving the cellulosic material from the conduit and having a level of liquid therein; and a slurry pump having an inlet for receiving material from the second vessel and an outlet operatively connected to the inlet of the digester. The digester may be one or more continuous or batch digesters.
The system preferably includes some form of metering device, such as a star-type or screw-type metering device, located between the outlet of the first vessel and the inlet of the conduit. A pressure isolation device, for example, a star-type pressure-isolation device, may also be located between the outlet of the first vessel and the inlet of the conduit, with or without the presence of a metering device.
The second vessel preferably substantially surrounds a peripheral portion of the conduit, and the second vessel has a top through which the conduit passes and a bottom having an outlet communicating with the inlet of the slurry pump. In a preferred embodiment, the second vessel is concentric with the first vessel and the conduit, and the outlet of the conduit is located below the top of the second vessel, but above the outlet of the second vessel.
The present invention also preferably includes a high pressure rotary transfer device having a low pressure inlet, a low pressure outlet, a high pressure inlet, and a high pressure-outlet. The high pressure inlet is operatively connected to the outlet of the second vessel and the high pressure outlet is operatively connected to the digester for feeding the comminuted cellulosic fibrous material slurry to the digester.
The second vessel of the present invention also preferably includes a conduit for introducing cooking liquor into the second vessel.
The first vessel is preferably a chip bin for storing and treating the cellulose chips, preferably a chip bin having one-dimensional convergence and side-relief geometry, for example, a DIAMONDBACK Chip Bin as described in U.S. Pat. Nos. 4,958,741; 5,500,083; 5,617,975; 5,628,873; and 5,700,355 and sold by Ahlstrom Machinery Inc. The first vessel may also be a horizontal Steaming Vessel having a screw conveyor, as sold by Ahlstrom Machinery. The first vessel may also have xe2x80x9cchiselxe2x80x9d-type geometry as disclosed in co-pending application Ser. No. 09/055,408 filed Apr. 6, 1998 now U.S. Pat. No. 6,199,299. The pressure in the first vessel is typically between about 0 and 5 bar gauge, preferably between about 0 and 2 bar gauge. The second vessel may also have one-dimensional convergence and side-relief geometry or chisel-type geometry to minimize the potential for bridging or plugging.
The present invention also includes a method of feeding a slurry of comminuted cellulosic fibrous material in liquid to a digester having an inlet utilizing a pre-treatment vessel, and a slurry pump having an inlet. The method comprises (a) pretreating the comminuted cellulosic fibrous material in the pretreatment vessel; (b) passing the pretreated material from the pretreatment vessel into a first conduit; (c) discharging the material from the first conduit into a vessel having a width dimension greater than the first conduit; (d) entraining the comminuted cellulosic fibrous material in liquid to form a slurry; (e) feeding the slurry to the inlet of the slurry pump; and (f) transporting the slurry to the inlet of the digester.
The invention preferably also includes a high-pressure transfer device having a low-pressure inlet and a high pressure outlet and the method further includes, between (e) and (f), (g) pumping the slurry with the slurry pump to the low-pressure inlet of the high-pressure feeder, and (h) discharging the slurry from the high-pressure outlet of the high-pressure feeder. The method may also include, between steps (c) and (d), (i) metering the flow of comminuted cellulosic fibrous material from the pretreatment vessel. The method may also further comprise passing the liquid from the low pressure outlet through an in-line drainer; pressurizing the liquid from the in-line drainer in a pressurizing device, and passing liquid from the pressurizing device to the digester; passing some liquid directly from the tank to just prior to the pressurizing device; and/or passing some of the pressurized liquid from the pressurizing device to the high pressure inlet to or outlet from the high pressure feeder.
The present invention also includes a system for feeding-comminuted cellulosic material entrained in liquid to a high pressure feeder connected to a digester, comprising: a vertical treatment vessel having a discharge at the bottom thereof; a metering device connected to the discharge of the treatment vessel; a generally vertical chute extending downwardly from the metering device; a high pressure feeder connected to a digester; a slurry pump which pumps a slurry of comminuted cellulosic material in liquid, the slurry pump having an inlet, the pump connected to the high pressure feeder; and a vessel having a width dimension greater than the width dimension of the chute, positioned concentric with the chute, and having a liquor level therein and an outlet operatively connected to the slurry pump inlet.
According to another aspect of the present invention there is provided a system for feeding comminuted cellulosic fibrous material in a liquid slurry to at least one digester, comprising: A device which slurries comminuted cellulosic fibrous material in liquid. A first pump for pumping slurry from the slurrying device to at least one digester. A second pump for supplying make-up liquid to the digester. A source of liquid for slurrying the comminuted cellulosic fibrous material. And, a single tank which performs both the function of controlling the level of liquid in the slurrying device, and the function of storing and supplying liquid in association with the source to the second pump, so that the first pump is properly and effectively substantially continuously supplied with liquid slurry, and the second pump with liquid.
Preferably the slurrying device includes a substantially vertical conduit, and the single tank substantially surrounds the conduit and is in liquid communication therewith. Typically the first pump is operatively connected to the substantially vertical conduit by a connecting conduit or transition; and there is a gap between the substantially vertical conduit and the connecting conduit or transition; and the single tank substantially surrounds the gap. Normally the gap has a substantially vertical dimension of between about 3-36 inches, and a screen or strainer is provided at the gap to minimize the amount of comminuted cellulosic fibrous material passing into the single tank through the gap. Optionally, the substantially vertical conduit is in further liquid communication with the single tank by at least one opening in the conduit vertically above and spaced from the gap.
The single tank may be substantially concentric (preferred), or offset, with respect to the substantially vertical conduit. In one embodiment a single tank comprises or consists essentially of a substantially right cylindrical upper portion and a substantially right circular one frustum lower portion. In another embodiment the single tank has a substantially right cylinder shape. In another embodiment the single tank is spaced and distinct from the slurrying device.
The system also preferably comprises a high pressure feeder connected to the first pump and having a low pressure outlet; an undesirable solids separator connected to the low pressure outlet; an in-line drainer connected to the separator; the in-line drainer having a first outlet line connected to the second pump, and a second outlet line connected to the slurrying device; and an automatically controlled flow-controlling valve in the second outlet line which controls the proportion of liquid from the in-line drainer flowing in the first outlet line compared to the second outlet line. Preferably the second outlet line, downstream of the valve, is substantially directly connected to both the substantially vertical conduit above the single tank and to the single tank.
The invention also comprises a method of feeding comminuted cellulosic fibrous material to a digester using a high pressure transfer device having a high pressure inlet and outlet, and low pressure inlet and outlet; comprising: a) Slurrying the material with liquid prior to feeding the slurry into the low pressure inlet. b) Returning liquid and any entrained material from the low pressure outlet to the low pressure inlet in a return system devoid of an in-line drainer and level tank. c) Pressurizing the slurry in the high pressure transfer device by pumping high pressure liquid into the high pressure inlet of the transfer device. And, d) passing the liquid from the high pressure outlet of the transfer device to the digester.
In the above described method b) may be further practiced using a return system also devoid of a centrifugal separator (sand separator); and/or also devoid of a surge tank. The method may further comprise removing tramp material from liquid circulating to or from the high pressure transfer device using a tramp metal trap. Further a) through d) may be practiced without a screen in the low pressure outlet.
According to another aspect of the present invention there is provided a feed system for a digester, comprising: A high pressure transfer device having a high pressure inlet and outlet, and low pressure inlet and outlet. A slurrying device connected to the low pressure inlet which slurries comminuted cellulosic fibrous material with liquid. A high pressure pump for pressurizing liquid being fed to the high pressure inlet. A connection between the high pressure outlet and a digester. A return system for returning liquid from the low pressure outlet to the slurrying device. And, the return system devoid of an in-line drainer and level tank.
The system as described above may further comprise a pump (e.g. a screw pump) not adversely affected by the presence of comminuted fibrous material in fluid pumped thereby, the pump connected between the return system and a digester. The low pressure outlet may be devoid of a screen. The return system may also be devoid of a centrifugal separator and/or surge tank. The system may further comprise a tramp material trap which removes tramp material from liquid circulating to or from the high pressure feeder.
Typically there is a pump between the slurrying device and the low pressure inlet, and the slurrying device may be a substantially vertical conduit substantially surrounded by a single tank which performs both the function of controlling the level of liquid and storing and substantially continuously supplying liquid to the pump (as described more fully above).
It is the primary object of the present invention to provide a simplified system and method for effectively feeding a comminuted cellulosic fibrous material slurry to continuous or batch digesters in the production of chemical cellulose pulp. This and other objects of the invention will become clear from the following detailed description of the invention, and the appended claims.